Facile solid-state synthesis of eco-friendly sodium iron silicate with exceptional sodium storage behaviour

Abstract

It is crucial to develop stable energy sources for rechargeable sodium-ion batteries using simple synthesis methods. Herein, we report a facile route for synthesizing phase-pure carboncoated Na 2 FeSiO 4 polyanionic cathodes using conventional solid-state methods at 700 °C under inert atmosphere. X-ray diffraction results reveal that there are no impurities in the highly crystalline Na 2 FeSiO 4 particles, resulting from the heat of combustion provided by the organic chelating agent. The electrochemical behaviour of Na 2 FeSiO 4 particles is tested within 1.5-4.5 V at 0.25 C. The Na 2 FeSiO 4 cathode delivered 119 mAh g -1 at 0.25 C and maintained ~ 85 % of its initial capacity after 200 cycles after activation process. Even at high current densities of 3.5 C, the material outperforms other orthosilicates-based cathodes reported with capacities of 55 mAh g -1 discharge capacity along with ~ 80% retention after 1,000 cycles. The enhanced performance of carbon-coated Na 2 FeSiO 4 particles is ascribed to the improved electronic conductivity by the incorporation of carbon and the presence of void space between the particles. This void space contains more electrolytes and eliminates the stress formed during the cycling process, thus improving stability even at high rates. This is the first report on obtaining phase pure metal orthosilicate material with negligible impurities using simple solid-state method along with such exponential electrochemical performances.

Constructing Safe and Durable High‐Voltage P2 Layered Cathodes for Sodium Ion Batteries Enabled by Molecular Layer Deposition of Alucone

“…It is well known that the surface morphology plays a vital role on electronic and ionic migration. [ 16–18,44 ] As nanostructured materials with uniform size distribution significantly reduce the pathway for Na‐ion migration, good electrochemical performance is expected from the NMM powders. [ 15,16 ] However, after 50 cycles of ALD and MLD coatings, the surface of the NMM particles became rough, as shown in Figure 1c,d, respectively.…”

“…The electrodes for ALD and MLD coating were prepared in accordance with the prior work. [ 2,17,18 ] The coating of ultrathin Al 2 O 3 on NMM electrodes was done using an ALD reactor (Thermal Gemstar 6XT, Arradiance, LLC, USA) at 115 °C in which trimethylaluminum (TMA) and H 2 O were used as the precursor and oxidizer, respectively. The purging time for water and TMA was set to 21 ms. On the other hand, the MLD of alucone on NMM electrode was also performed at 100 °C by alternatively introducing TMA and ethylene glycol (EG).…”

“…[ 3 ] Materials such as P2‐NaMO 2 (M = Fe, Cr, Mn, Co, V, and Ni), Na 2/3 Ni 1/3 Mn 2/3− x Ti x O 2 , Na 2/3 (Ni 1/3 Mn 2/3 )O 2 , Na 0.67 Mn 0.65 Fe 0.2 Ni 0.15 O 2 , Na 0.66 Fe 1/2 Mn 12/ O 2 , and MCN‐type materials such as Na 0.45 (Mn 0.66 Co 0.11 Ni 0.22 )O 2 , Na 0.67 (Mn 0.65 Co 0.2 Ni 0.15 )O 2 , and Na 0.66 (Mn 0.54 Co 0.13 Ni 0.13 )O 2 have been studied and characterized in SIBs. [ 1,2,9–21 ] These materials have high initial capacities but are only stable below 4.3 V versus Na/Na + . Above 4.3 V, P2‐type cathodes undergo an irreversible phase transition to O2‐type which causes a large capacity loss upon cycling.…”

“…[ 1,19 ] Carbon coatings are well known to improve stability and cycling performance of cathodes, but this creates a layer of inactive material on the surface of the cathode, which reduces the specific capacity. [ 2,17,29–32 ] Instead of carbon coating, a metal oxide coating can offer the same protection against dissolution into the electrolyte and improve cyclability up to 4.5 V while also adding capacity. [ 15,16,18,33 ] Conventional methods such as ball milling, sol–gel, and hydrothermal synthesis have been used to coat metal oxides on cathode materials.…”

An ion conductive polyimide encapsulation: New insight and significant performance enhancement of sodium based P2 layered cathodes

“…[15][16] However, these materials displayed poor ability to store sodium ions into their structures and severe capacity fading upon cycling. 17,18 Unlike their Li + analogue, layered Na + host materials do not suffer from cation mixing between sodium and transition metal ion layers due to the larger atomic radius of sodium (Na + -1.02 Å) than that of lithium (Li + -0.76 Å), leading to a well-developed layered structure. 19 In general, layered Na based intercalation materials could be mainly categorized as O3-and P2-type structure, in which Na-ions are occupying at octahedral and prismatic sites, respectively.…”